This invention relates to a sheet post-processing apparatus for selectively applying a process such as aligning or binding to sheets sent from an image forming apparatus such as a laser printer or copier, and also relates to an image forming apparatus equipped with this sheet post-processing apparatus.
Conventionally, as shown in FIG. 33 and FIG. 34, it is known that there is a sheet post-processing apparatus 201 mounted to an image forming apparatus such as a laser printer or a copier. The sheet post-processing apparatus is equipped with an intermediate tray 222 to support an upstream side of a sheet fed from an image forming apparatus 200 and discharged by tray discharge rollers 214 and 215, and a stack tray 225 established at downstream of the intermediate tray 222 and below with the level 221 (FIG. 35(b)) being vertically moveable in the Z direction. The Sheet once discharged in a state of straddling both trays as shown in FIG. 35(a) is aligned by forcibly transporting them to an alignment reference using an abutting plate 217 and a position plate 223 by a discharge alignment belt 216 and a second alignment belt 302. While maintaining the sheet straddling both trays, a sheet bundle is formed by sequentially discharging the sheet as shown in FIG. 35(b). Then, after a post-processing of the sheet bundle such as stapling with the stapler 224, the sheet bundle is pressed by discharge means composed of the abutting plate 217 as shown in FIG. 35(c), and the apparatus discharges the sheet sequentially to the stacking tray 225 (Japanese Patent No. 08-9451). Note that a trailing edge of the sheet on the stack tray 225 is regulated by the level 221 relative to the intermediate tray 222 (a regulating plate 226).
However, in the conventional sheet post-processing apparatus described above, the sheet is curled in the transport direction (hereinafter referred to as the “feed direction”) at a point where the sheet is fed from the image forming apparatus.
As described above, after applying the stapling to the sheet with a curl in the feed direction, the sheet is transported by discharge means such as the abutting plate 217 and the discharge rollers, thereby sequentially being discharged to the stack tray 225, as shown in FIG. 35(b) to FIG. 35(c). In this case, a discharging drive force applied by the abutting plate 217 and the discharge rollers is absorbed by the curl in the sheet feed direction. That is, even if the discharging drive force is applied to the sheet, the process only increases the curling, thereby causing a problem that the sheet is not fully discharged to the stack tray 215.
Thus, in view of resolving the problems related to the conventional technology, this invention provides an apparatus that can securely discharge a sheet bundle to a stack tray after applying a post-process such as stapling to the sheet bundle.